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  Research theme

Overview of research theme in our group where we combine the synthesis of 2D materials such as graphene with fundamental studies of colloidal phases and flow behaviour to arrive at industrially-adaptable manufacturing and fabrication methods in developing efficient graphene-based platforms for clean energy, chemical separations and micro-/nano-fluidics.

Graphene-based energy materials and devices program: Most of the research activity centers around exfoliation of graphite in liquid phase predominantly as a highly oxidized and water soluble precursor – graphene oxide (GO). Graphite is a naturally occurring mineral deposit which serves as a cheap source for these advanced materials, thus highlighting a significant value addition to this mineral resource. Graphene-based materials because of their monoatomic thickness possess massive surface area, large electrical conductivity, mechanical flexibility and can be processed easily in the fluid phase. The energy program endeavours to develop novel energy storage materials, architectures and devices in the space of super-capacitors and batteries.

Miniaturization of energy storage devices: Microarchitecture plays a significant role in enhancing the power and energy density of super-capacitor devices. If two electrodes can be spaced very close to each other with micron-scale resolution and the dimensions of each electrode could be miniaturized, electrode kinetics will be dramatically enhanced and active electrode surface area could be much better utilized. The upshot of miniaturization is that the reduced dimensions not only have very large energy and power densities, but also can be densely packed in a given area. Graphene-oxide (GO), which is essentially an insulator, can be processed into continuous films and conductive pathways in the GO film can be imprinted by different irradiation techniques such by using laser, UV radiation and ion-beams enabling precise pattering methodologies [1]. A significant aspect of the program will focus on the chemical reduction mechanisms, microstructure and carbon structure evolution, and how patterning approaches could be developed based on these fundamentals. The second aspect of the program will focus on measurement of electrochemical properties in wide ranging electrolytes to unearth how carbon structure, electrolytes and microarchitecture affect energy and power density [2]. The third aspect of the program will focus on device construction, integration and proto-typing. The significance of the program is that while the microelectronic industry has made rapid progress in following the Moore’s law, is it possible that the energy storage sector can follow suit if we adapt micro-fabrication strategies in energy storage technologies?

Skills to be acquired in this project: micro-/nano-fabrication, electrochemistry, system design for energy storage devices

MOF/Graphene Composites: Metal Organic Frameworks (MOFs) are crystalline, open-porous materials consisting of metal ions or metal-oxo units coordinated by electron donating organic ligands and possess very high surface area (~7000 m2/g)  well defined pore sizes and tailorable structure. However, their electrochemical charge storage properties are poor because of their poor electron conductivity. The research theme will explore the synthesis of different MOFs and formation of intimately mixed composites with graphene in bulk scale quantities. This will be followed by characterization of the material and investigation of their charge transport, mass transport and electrode kinetics using a variety of electrochemical techniques such as cyclic voltammetry, impedance spectroscopy, galvanostatic polarization, and spectro-electrochemistry. Given the rich family of MOFs known today and the ability to tailor their structure during synthesis there is potential for generation of extensive fundamental data and applications to be realized for high energy and high power density super-capacitor materials [3].

Graphene-based fluidic systems program - from compact micro-/nano-fluidic devices to large area filtration membranes:  The fluidics program deals with fundamental aspects of fluid-phase processing of 2D materials. and applied aspect of fluid and mass transport through layered 2D structures in the form of films, granules and micro-/nano-fluidic devices.

Graphene membrane development and application: GO has rich colloidal phase behaviour because of its large lateral dimension to thickness ratio and exhibits phase transitions from isotropic to nematic liquid crystalline phases [4] depending upon concentration of GO and pH. GO is also a very flexible molecule with a small persistence length and non-conservatively can be considered as a polymeric fluid. Using techniques such as orientation-mapped polarized light microscopy and rheology we determine how these materials can be processed into macroscopic structures such as films, droplets, granules or fibers by industrially-relevant manufacturing approaches [5]. Based on fundamental understanding between processing and property we have developed scalable roll-to-roll process for the manufacture of multi-layer graphene-based membranes [6]. Graphene based membranes have unique combinations of chemical inertness, fouling resistance, fast water transport in the liquid and vapour phase, nanoscale capillaries, tunable molecular weight cut-off with tremendous potential in nanofiltration and pervaporation that could solve separation problems for e.g. in recovery of precious metals and expensive chemicals in challenging environments and dehydration of organic-water mixtures. Given our demonstrated ability to manufacture these membranes with massive scalability, we will next focus on realizing these applications. Additionally through collaborations with simulation experts we will unravel the fundamental aspects of molecular transport through these membranes structures which has been the subject of intense research in the past few years [7].

Skills to be acquired in this project: polarized light microscopic imaging, rheology, membrane fabrication, membrane transport

Engineered Adsorbents: Emanating from our ability to process the solution-stabilized graphene sheets is our ability to easily form 3D structures such as granules by coating over an existing granular structure such as a sand grains or an adsorbent granule. We have previously demonstrated the utility of these granular structures as filtration materials in column-based filtration [8]. Given that the coating chemistry can be tuned by the functional groups and mass transport controlled by the porosity of the assembled structures, a wide variety of pollutants could be targeted. Among them sequestration of trace organics and mercury from pollution streams will be of immediate significance. It is expected that significant industrial interest can be generated in this research program.

Skills to be acquired in this project: Graphene chemistry, adsorptive separation technologies

Micro-/Nano-Fluidics: Graphene-based multilayer thin films are exciting new materials for fluidic systems because these films form ensemble nano-capillaries between each individual graphene sheet of ~ 1nm regardless of the size of the graphene microplates and the size of the continuous films. These films can be positioned directly on a substrate at precise locations with dimensional control of hundreds of microns by simple masking processes, but these films contain assembled nanoscale capillaries which are permselective [9]. The abilities to precisely place these nanocapillaries enables us to integrate nanofluidics with microfluidics, thus opening up a host of possibilities in fundamental understanding of ion-transport behaviour such as electrosmosis, electrophoresis and ion-current rectification [10], while empowering us to effectively use these nanoscale phenomena in chip-based separations by interfacing with microfluidics and surface functionalization chemistries.

Skills to be acquired in this project: Microfluidics, nanofluidic transport measurement.


References (published by our research group along with collaborators)

[1] D. E. Lobo, J.Fu, T.Gengenbach, M. Majumder, "Localized Deoxygenation and Direct Patterning of Graphene Oxide by Focused Ion Beams” Langmuir, 2012, 28, 41,14815–14821

[2] D.E.Lobo, P.Chakraborty-Banerjee, C.Easton, M.Majumder, “Miniaturized In-plane Electrode Systems of Reduced Graphene Oxide with Enhanced Energy and Ultra-high Power Densities by Focused Ion-beam Engineering” Advanced Energy Materials, (in press)

[3] P. Chakraborty-Banerjee, D.E.Lobo, R.Middag, W.K.Ng, M.Majumder, “Electrochemical Capacitance of Ni-doped MOF-5 and reduced graphene oxide composites: More than the sum of its parts”, ACS Applied Materials and Interfaces, 2015,7,6,3655-64

[4] R.Tkacz, R.Oldenbourg, S.B. Mehta, A. Verma, M.Miansari, M.Majumder, "pH Dependent Isotropic to Nematic Phase Transitions in Graphene Oxide Dispersions Reveal Droplet Liquid Crystalline Phases", Chem.Commun, 2014,50, 6668-6671

[5] R.Tkacz, R.Oldenbourg, A.Fulcher, M.Miansari, M.Majumder, "Capillary-Force Assisted Self-Assembly (CAS) of highly Ordered and Anisotropic Graphene-Based Thin Films", J.Phys.Chem.C, 2014, 118 (1), 259–267

[6] M.Majumder, A. Akbarivakilbadi, “A method for producing graphene and graphene oxide membranes”, Australian Provisional Patent, 21 Nov, 2014

[7] M.Majumder and B.Corry, “Anomalous Decline of Water Transport in Covalently Modified Carbon Nanotube Membranes”, Chem.Commun, 2011, 47, 7683-85

[8] W.Gao, M. Majumder, L. Alemany, T. Narayanan, M. Ibarra, B.K. Pradhan, P.M. Ajayan, “Engineered Graphite Oxide Materials for Application in Water Purification” ACS Applied Materials and Interfaces, 2011,3, 6,1821–1826

[9] M.Miansari, J.R.Friend. P.Chakraborty-Banerjee, M.Majumder, L.Y.Yeo, "Graphene-based planar nanofluidic rectifier", J. Phys. Chem. C, 2014, 118 (38), 21856–21865

[10] S.Martin, A.Neild, M.Majumder,"Graphene-based ion rectifier using macroscale geometric asymmetry", APL Mat. 2, 092803, 2014 - Special Topic in 2D Materials.

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